Transmissions for Class 6 through 8 commercial line haul and off road trucks are rugged and reliable. Some such transmissions provide more than one million miles of service; however the transmissions can be heavy. Some heavy duty (HD) truck transmissions weigh from about 500 to about 800 pounds. Thirty percent of the weight of typical existing HD transmission is attributed to the gears. Some currently made gears are fabricated from one piece of solid, carburized steel (e.g., AISI 8620). First, a solid steel billet is forged into a steel pancake. Second, the gear teeth are machined into the pancake. More than 10 percent of the steel is machined away from the pancake and ultimately discarded or recycled. The machined gear is carburized for as long as 13 hours in a furnace that runs continuously. The carburized gear is hardened and tempered in another furnace. Gears fabricated in this existing manner can weigh from several pounds to about 32 pounds depending on the pitch diameter and axial length. Heavy gears can be a factor that limits fuel economy in large commercial trucks. Gear weight in a transmission can also limit the performance of military and commercial helicopters.
The production of gears fabricated in the traditional manner described above may contribute to the consumption of energy by carburizing and heat treating/tempering furnaces that operate continuously. Some heat treating/tempering furnaces may emit carbon dioxide into the environment.